Sharing music via quality audio equipment is one of the coolest experiences you can have with friends. It's so fulfilling to see a a pal sit in the sweet spot and actually "hear" their favorite song for the fist time! You can tell when they are audibly aware of everything they've been missing...their eyes light up and the corners of their mouth crack into a grin...and you have done your duty as an "audiophile." It's all about sharing the passion!
Now, to get on with a useful answer to the original question of, "How do I tell visitors not to touch my stuff without sounding like a condescending a**hole?"
When you're ready to start the session, you can say with a smile and in a jovial way something like, "At risk of sounding like a condescending a**hole, you must be made aware of the following. Do Not touch anything. LOL (actually laugh out loud here). I know you would never do that, but you'd be surprised at what people are capable of. Nobody has done it here, cause our friends aren't morons, LOL, but I've heard horror stories of guests accidentally breaking people's gear. Anyway...getting that close to the speaker doesn't do anything for the sound. For the best experience, you want to be here (point to your seat in the sweet spot). Get cozy, you're going to love this."
As they take a seat, say something like, "Tell me the fist song that comes to your mind in 5,4,3,2,1." When they blurt out a song, don't second guess it, just pull it up on your streamer and push play. I find this method more entertaining than putting people on the spot for their favorite song or album or artist. It's fun to discuss those things, but the "go with your gut" moment is a fun way to get things started.
Never start with your favorite song or artist or album...this only makes you seem like a condescending a**hole. I like to let people listen to their first song, and then say, "Ok, what's next?" Usually, they have been thinking of the song they really wanted to hear while their listening to the first song.
If you have multiple guests who want to listen, the next person will have their pick ready. And the next. And the next. I find it fun to go from guest to guest for each subsequent song. It's a great way to get exposed to cool music I would never hear on my own and it keeps guests engaged and interested. As they realize the true potential of your system, the song picks get more and more curated. Meaning, the guests put a lot of thought into a song that will have it's full potentially become an absolute revelation when it's piped through your gear. As we go from one person's to another's pick, I make sure to include myself in the rotation. This is where I drop in some mind-blowing, ear-awakening gems.
In these moments, it's fun to enjoy some whisky, wine, beer, or whatever your social lubricant of choice may be. Turning what is often a solo experience into one that can be shared and enjoyed with friends is very rewarding and I find that people want to come back!
Congrats! Instead of becoming a condescending, audiophile a**hole, you are now the life of the party. And your gear is safe ;)
Cheers.